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Comparison of dating methods for paleoglacial reconstruction in Central Asia
Stockholm University, Faculty of Science, Department of Physical Geography. (Geomorphology and Glaciology)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reconstruction of former Central Asian glaciers extents can provide valuable information about past atmospheric circulation variations. These extents, often marked by terminal moraines, need to be chronologically constrained. Cosmogenic nuclide exposure (CNE) dating is widely used to directly date moraines. In addition, there is increasing interest on using optically stimulated luminescence (OSL) techniques for dating glacial landforms. This thesis focuses on the methodological aspects of directly dating glacial landforms to perform paleoglacial reconstructions in Central Asia, with an emphasis on OSL dating.

For OSL dating of sediments from glacial settings, it is important to measure the luminescence signal at the single grain scale, because the sediments are likely affected by partial bleaching due to short light exposure during glacial or glaciofluvial transport. The use of an Electron Multiplying Charges Coupled Device (EMCCD)-based imaging system for single grain OSL measurements would offer larger flexibility in light stimulation and sediment type, compared to the current Single Grain Risø reader. An automated image processing procedure has been developed to compensate for sample carrier displacement over repeated measurements and for attributing pixels to each grain for signal integration when using this imaging system. However, significant cross talk contamination, demonstrated by laboratory and simulation experiments, prohibits accurate single grain luminescence measurements. Preliminary experiments using a basic image processing algorithm show good potential for software correction solutions.

Paleoglacial reconstructions conducted in the Altai Mountains, Central Asia, using both CNE and OSL dating demonstrate that luminescence measurements of glaciofluvial sediments performed at the multi-grain scale result in large age overestimates, and that single grain measurements allow for more accurate dating of glacial landforms. However, uncertainties remain that are related to the model used for extracting equivalent doses for well-bleached grains and to fading corrections when using feldspar minerals. The timing of glaciation can be inferred from scattered CNE moraine boulder ages if most of the ages are concentrated within a few thousand years, with only few ages clearly older or younger. Overall, combining CNE and OSL techniques for dating a glacial landform is a powerful approach for producing robust glacial chronologies, despite uncertainties inherent to each technique.

Paleoglacial reconstructions from the Altai Mountains indicate Marine Isotope Stage (MIS) 2 and MIS 4/late MIS 5 local Last Glacial Maximums. In Central Asia, in addition to a regional MIS 2 glaciation, previous studies indicate a period of major glacial advances during MIS 3 that is out of phase with global ice volume records. However, most MIS 3 glacial chronologies from Central Asia are based on too few or too heavily scattered CNE data sets, or on OSL or Electron Spin Resonance (ESR) ages for which partial bleaching has not been properly investigated. Hence, at this stage, chronological evidence is insufficient to demonstrate a regional MIS 3 glaciation in Central Asia.

Surge-related glacial features identified in the Russian Altai also highlight the importance of conducting detailed geomorphology and sedimentology studies to understand former ice dynamics, which is essential for inferring appropriate paleoclimate information from paleoglacial reconstructions.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University , 2016. , 55 p.
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 58
Keyword [en]
Paleoglaciation, Optically stimulated luminescence dating, Cosmogenic nuclide exposure dating, EMCCD camera
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-132915ISBN: 978-91-7649-466-0OAI: oai:DiVA.org:su-132915DiVA: diva2:955904
Public defence
2016-10-14, William-OIssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-09-21 Created: 2016-08-26 Last updated: 2016-09-13Bibliographically approved
List of papers
1. Single-grain dose-distribution measurements by optically stimulated luminescence using an integrated EMCCD-based system
Open this publication in new window or tab >>Single-grain dose-distribution measurements by optically stimulated luminescence using an integrated EMCCD-based system
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2015 (English)In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 29, 70-79 p.Article in journal (Refereed) Published
Abstract [en]

We report on the feasibility of assessing single-grain dose-distributions by using an EMCCD-based imaging system with complementary analysis software. Automated image-processing was successfully applied to compensate sample motion and for grain identification. Following a dose recovery test, 74% of the grains were recognized successfully, and 44% exhibited a suitable OSL dose response behavior to interpolate an equivalent dose value, and a central dose recovery ratio of 1.038 was obtained.

Keyword
Spatially resolved luminescence, OSL, TL, Luminescence dating, Lexsyg reader
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-120073 (URN)10.1016/j.quageo.2015.06.009 (DOI)000358629300008 ()
External cooperation:
Available from: 2015-09-07 Created: 2015-09-01 Last updated: 2016-08-30Bibliographically approved
2. Investigation of cross talk in single grain luminescence measurements using an EMCCD camera
Open this publication in new window or tab >>Investigation of cross talk in single grain luminescence measurements using an EMCCD camera
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2015 (English)In: Radiation Measurements, ISSN 1350-4487, E-ISSN 1879-0925, Vol. 81, 163-170 p.Article in journal (Refereed) Published
Abstract [en]

Highly sensitive electron multiplying charges coupled devices (EMCCD) enable the spatial detection of luminescence emissions from samples and have a high potential in single grain luminescence dating. However, the main challenge of this approach is the potential effect of cross talk, i.e. the influence of signal emitted by neighbouring grains, which will bias the information recorded from individual grains. Here, we present the first investigations into this phenomenon when performing single grain luminescence measurements of quartz grains spread over the flat surface of a sample carrier. Dose recovery tests using mixed populations show an important effect of cross talk, even when some distance is kept between grains. This issue is further investigated by focusing just on two grains and complemented by simulated experiments. Creation of an additional rejection criteria based on the brightness properties of the grains is inefficient in selecting grains unaffected by their surroundings. Therefore, the use of physical approaches or image processing algorithms to directly counteract cross talk is essential to allow routine single grain luminescence dating using EMCCD cameras.

Keyword
Luminescence, Spatially resolved, EMCCD camera, Cross talk, Single grain
National Category
Subatomic Physics Geology
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-123808 (URN)10.1016/j.radmeas.2015.01.017 (DOI)000364502700025 ()
External cooperation:
Conference
14th International Conference on Luminescence and Electron Spin Resonance Dating, Montreal, Canada, July 07-11, 2014
Available from: 2015-12-11 Created: 2015-12-07 Last updated: 2016-08-30Bibliographically approved
3. Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai
Open this publication in new window or tab >>Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai
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2016 (English)In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 149, 288-305 p.Article in journal (Refereed) Published
Abstract [en]

The Southern part of the Russian Altai Mountains is recognized for its evidence for catastrophic glacial lake outbursts. However, little is known about the late Pleistocene paleoglacial history, despite the interest in such reconstructions for constraining paleoclimate. In this study, we present a detailed paleoglaciological reconstruction of the Chagan Uzun Valley, in the Russian Altai Mountains, combining for the first time detailed geomorphological mapping, sedimentological logging, and in situ cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. The Chagan Uzun Valley exhibits the most impressive glacial landforms of this sector of the Altai, with extensive lobate moraine belts deposited in the intramontane Chuja Basin, reflecting a series of pronounced former glacial advances. Observations of “hillside-scale” folding and extensive faulting of pre-existing soft sediments within the outer moraine belts, together with the geomorphology, strongly indicate that these moraine belts were formed during surge-like events. Identification of surge-related features is essential for paleoclimate inference because these features correspond to a glacier system that is not in equilibrium with the contemporary climate, but instead largely influenced by various internal and external factors. Therefore, no strict relationship can be established between climatic variables and the pronounced distal glacial extent observed in the Chagan Uzun Valley/Chuja basin. In contrast, the inner (up-valley) glacial landforms of the Chagan Uzun valley were likely deposited during retreat of temperate valley glaciers, close to equilibrium with climate, and so most probably triggered by a general warming. Cosmogenic ages associated with the outermost, innermost, and intermediate stages all indicate deposition times clustered around 19 ka. However, the actual deposition time of the outermost moraine may slightly predate the 10Be ages due to shielding caused by subsequent lake water coverage. This chronology indicates a Marine Isotope Stage (MIS) 2 last maximum extent of the Chagan Uzun Glacier, and an onset of the deglaciation around 19 ka. This is consistent with other regional paleoclimate proxy records and with the Northern Hemisphere glaciation chronology. Finally, this study also highlights the highly dynamic environment in this area, with complex interactions between glacial events and the formation and drainage of lakes.

Keyword
Altai, Paleoglaciation, Surging glacier, Geomorphology, Sedimentology, 10Be and 26Al surface exposure dating, Moraines
National Category
Physical Geography Climate Research
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-132960 (URN)10.1016/j.quascirev.2016.07.032 (DOI)
External cooperation:
Funder
Swedish Research Council, 2009-4411Swedish Research Council, 2011-4892
Available from: 2016-08-26 Created: 2016-08-26 Last updated: 2016-08-30Bibliographically approved
4. Major glaciation in Central Asia during MIS 3: reality or dating artefact?
Open this publication in new window or tab >>Major glaciation in Central Asia during MIS 3: reality or dating artefact?
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Previous investigations have concluded that a period of major glacial advances occurred during Marine Isotope Stage (MIS) 3 (57-29 ka) in Central Asia, out of phase with global ice volume records. We have re-examined the Kanas moraine complex in the Altai Mountains, where an MIS 3 glaciation has been previously inferred. New cosmogenic exposure and single grain luminescence ages indicate that the Kanas complex was formed during MIS 2 (29-12 ka); we regard the initial MIS 3 interpretation as a result of dating artefacts. Building on this example, we reanalyze chronological data associated with proposed major MIS 3 glacial advances in Central Asia (24 sites). We find that chronological data do not allow glaciation timing inferences for most of the sites, and that chronological evidence for major MIS 3 glacial advance only exists at one site.

Keyword
glaciation, MIS 3, Kanas Valley, IRSL, cosmogenic exposure dating
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-132962 (URN)
External cooperation:
Funder
Swedish Research Council, 2009-4411Swedish Research Council, 2011-4892
Available from: 2016-08-26 Created: 2016-08-26 Last updated: 2016-08-26

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